X-ray photographing has been performed in various medical fields for the purpose of inspection.
At the time of performing the X-ray photographing, a scattered radiation is generated when a radiated X-ray is transmitted through a medium.
The scattered radiation causes a decrease in an image contrast and an increase in noise. Therefore, it is preferable to detect only a primary radiation having useful image information.
Generally, an anti-scatter grid is used in order to allow the primary radiation to be transmitted and block (or attenuate) the scattered radiation. Korean Patent Laid-Open Publication No. 10-2011-0063659 or Korean Patent Laid-Open Publication No. 10-2011-0089134 has disclosed a technology of applying a grid to a mammography. Here, the mammography is an X-ray photographing apparatus used to detect breast cancer, lesion, and micro-calcification.
As disclosed in the patent laid publications mentioned above, the grid is positioned between a target to be photographed (for example, ‘breast’) and a detector. In addition, the grid reciprocates so as to appropriately perform a function thereof. The present invention relates to a reciprocating technology of the grid.
The related art for reciprocation of a grid 141 will be described with reference to a schematic plan view of FIG. 1.
A moving device 143 is required in order to let the grid 141 reciprocate.
The moving device 143 includes a pair of coupling members 143a and 143b, a guide shaft 143c, a moving source 143d, a pair of compression springs 143f-1 and 143f-2, and a pair of support members 143g and 143h. 
The coupling members 143a and 143b include long guide holes GH1 and GH2 formed therein, respectively, in a movement direction (horizontal direction) (See an arrow) of the grid 141. Front ends of the coupling members 143a and 143b are coupled to the grid 141. In addition, one coupling member 143a has a coupling groove JS formed at a rear end thereof.
The guide shaft 143c has a pair of guide bars 143c-1 and 143c-2 long in a horizontal direction.
The guide bars 143c-1 and 143c-2 are inserted into the guide holes GH1 and GH2 of the coupling members 143a and 143b, respectively. Therefore, horizontal direction of the coupling members 143a and 143b is guided by the guide bars 143c-1 and 143c-2.
The moving source 143d includes a motor 143d-1 and a transfer member 143d-2.
The motor 143d-1 generates moving force of the coupling members 143a and 143b. In FIG. 1, the moving force is applied leftward.
The transfer member 143d-2 has a front end inserted into the coupling groove JS of the coupling member 143a and a rear end connected to the motor 143d-1. Therefore, the transfer member 143d-2 transfers the moving force generated in the motor 143d-1 to the coupling member 143a. 
The compression springs 143f-1 and 143f-2 are installed in a form in which the guide bars 143c-1 and 143c-2 are inserted thereinto, respectively. These compression springs 143f-1 and 143f-2 apply elastic force to the coupling member 143a rightward.
The support frames 143g and 143h support a bottom surface of the grid 141.
Reciprocation of the grid 141 performed in the configuration as described above will be described.
The moving force generated by the motor 143d-1 is transferred to the coupling member 143a through the transfer member 143d-2. Therefore, the coupling members 143a and 143b and the grid 141 move leftward. In addition, the compression springs 143f-1 and 143f-2 are compressed. When the moving force from the motor 143d-1 subsequently disappears, the coupling members 143a and 143b and the grid 141 move rightward by elastic restoring force of the compression springs 143f-1 and 143f-2.
Meanwhile, it is preferable that the grid 141 moves at a velocity close to a constant velocity in order to obtain appropriate image quality.
However, the related art as described above has the following factors hindering the constant velocity movement of the grid 141.
First, lengths of the compression springs 143f-1 and 143f-2 are short due to a limitation in installation. Therefore, a deviation between early restoring force (restoring force at a point in time in which the compression springs are maximally compressed) and later restoring force (restoring force immediately before the grid returns to its original position) is large.
Second, the front end of the transfer member 143d-2 is inserted into the coupling groove JS of the coupling member 143a with a clearance interposed therebetween. Therefore, vibrations, noise, and the like, are instantaneously generated due to a backlash between the transfer member 143d-2 and the coupling member 143a at the early stage of generation of the moving force of the motor 143d-1.
Therefore, the grid 141 may not move at a constant velocity within a moving section (about 12 mm). In addition, when the transfer member 143d-2 strikes the coupling member 143a, vibrations and noise are generated.
In addition, in the mammography, the grid 141 may be stood to be inclined at a predetermined angle depending on a photographing angle of a breast. In this case, the support frames 143g and 143h may not stably support the grid 141.